Sun lamp shadows too sharp
Use the Lamp > Shadow > Soft Size setting. By default for a sun lamp, it is set to 0.1, which produces sharp shadows. Increasing that number will make the shadows cast by that lamp softer.



Note: in order for you to see the softer shadows in your render, you need to increase the Lamp > Shadow > Samples value to something higher than 1.

Example: Soft Size = 0.1



Example: Soft Size = 5.0